The present invention relates to a power breaker apparatus which quickly detects an abnormal current to break a power supply to a load when the abnormal current is fed by a short-circuit of the load.
As shown in FIG. 1, the conventional power breaker apparatus comprises a permanent fuse PF and resistors R connected in parallel to the fuse which are connected between a short time delaying main breaker B and a plurality of shunt breakers F.sub.1 to F.sub.n.
The permanent fuse PF suddenly increases its resistance when fault current is passed. The relation of a resistance R.sub.PF of the conventional permanent fuse PF and the parallel resistance R is R.sub.PF &lt;R whereby the ratio is controlled to pass all of the current through the permanent fuse PF in the normal state.
For example, when a short-circuit is caused in the circuit of the shunt load F.sub.1, the fault current is passed through the permanent fuse PF to increase suddenly the inner resistance of the permanent fuse to be several hundreds times to the initial resistance whereby the fault current is reduced and the limiting current is fed through the parallel resistor R to the shunt breakers F.sub.1 and accordingly, the shunt breaker F.sub.1 is actuated.
FIG. 2 shows the current limiting condition of the fault current. When the fault current I.sub.pros is fed, the inner resistance of the permanent fuse PF is suddenly increased to perform the current limiting operation to control the peak value of the current to I.sub.pfc. The resistance of the permanent fuse PF is greater than the parallel resistance R whereby the fault current I.sub.pfr is continuously passed through the permanent fuse PF and the resistor R to operate the shunt breaker F.sub.1.
The conventional power breaker apparatus has the above-mentioned structure and the presumed short-circuit current maximum peak value I.sub.c is limited to the current limiting maximum peak value I.sub.pfc resulted by the permanent fuse PF. However, at the current limiting operation, there is a problem which causes an abnormal voltage between the parallel resistor R and the connecting conductor so as to damage the parallel resistors by arcing.